Spun metal form used to manufacture dual alloy turbine wheel

ABSTRACT

A spun metal form used to manufacture a dual alloy turbine wheel. The spun metal form prevents braze alloy contamination of the hub/casting interface by relocating the braze joint away from the interface. The spun metal form allows for the re-working of components after failed vacuum brazing and increases the time to failure of dual alloy turbine wheels.

BACKGROUND OF THE INVENTION

The present invention generally relates to dual alloy turbine wheelsand, more particularly, to spun metal forms used to manufacture dualalloy turbine wheels.

Turbine wheels comprising two distinct alloys have been used extensivelyin gas turbine engines. Dual alloy wheels have been used to address theneed for hubs and castings having different material properties. Dualalloys have been used to provide turbine wheel hubs having one set ofmaterial properties and turbine wheel castings having another set ofmaterial properties. Turbine wheel hubs have been formed from alloysthat have high tensile strength and low cycle fatigue resistance.Turbine wheel castings, which are exposed to the higher temperatures ofthe gas path and higher centrifugal loads, have been formed from alloysthat have high stress rupture and creep resistance. The two dissimilaralloy parts have been joined by hot isostatic pressing to form dualalloy turbine wheels.

Hot isostatic pressing (HIP) utilizes an autoclave and a pressuretransfer medium, such as inert argon gas, to facilitate diffusionbonding of the two dissimilar metals. Vacuum sealing the interfacebetween the casting and the hub is necessary for acceptable diffusionbond formation. Metal or ceramic shaped containers have been used tocompletely enclose and vacuum seal the dual alloy components during HIP.Unfortunately, these methods are unsuitable for some applications due tocontainer leakage and geometric limitations.

Other methods for producing dual alloy turbine wheels by HIP have beendisclosed in U.S. Pat. No. 4,581,300. In this method, the casting andhub are assembled. A sealing plate is then electron-beam welded andvacuum brazed to the casting. Although this method may be used to vacuumseal the interface, braze alloy contamination of the interface iscommon. Braze alloy contamination in the structural region of the partis unacceptable in some applications and results in poor fieldperformance. Using these methods, scrap due to braze alloy contaminationhas been reported to be about 20% and the associated manufacturing costto be about $500,000/year.

Another HIP method is described in U.S. Pat. No. 4,603,801. In thismethod, the pressure transferring medium comprises a granular glassmedium. The interface is isolated from the pressure transferring mediumby a stainless steel interference fit seam isolator. Although brazealloy contamination of the dual alloy interface may be prevented byusing these methods, the disclosed processes are not useful for manyapplications.

Another method for preventing braze alloy contamination is disclosed inU.S. Pat. No. 4,796,343. In this method, annular braze traps are used toprevent braze contamination of the interface. Braze trap formationrequires machining of the hub and casting. Unfortunately, the machiningnecessary to form the braze traps is expensive and exacting. Because thecasting is brazed to the hub, the re-working of leaking assemblies isnot possible and further increases production costs.

An expendable spun metal form capable of preventing braze alloycontamination is needed. Also, there is a need for improved methods ofpreventing braze alloy contamination of a dual alloy interface. A methodis needed wherein braze trap machining is not necessary. Moreover, thereis a need for a method wherein the hub and the casting of a leakingassembly can be re-worked.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an apparatus used to manufacturea dual alloy object comprises a formed can. The formed can flange isvacuum brazed to the dual alloy casting flange. By locating the brazeinterface away from the casting hub interface, braze alloy contaminationis prevented.

In another aspect of the present invention, an apparatus used toposition a braze bead on a dual alloy assembly comprises a form can; andan annular form flange extending radially out from and integral to theform can, the annular form flange having a flange edge, the dual alloyassembly having an interface edge, and the apparatus capable of being incontact with the dual alloy assembly such that the form can is incontact with the interface edge and such that a distance between theflange edge and interface edge is about 0.090 inches.

In yet another aspect of the present invention, an apparatus used tomanufacture a dual alloy turbine wheel comprises a form can; and anannular form flange extending radially out from and integral to the formcan, the annular form flange comprising a nickel-based superalloy, thedual alloy turbine wheel having an interface and a casting flange, theapparatus capable of being in contact with the dual alloy turbine wheelsuch that the form can is in contact with an edge of the interface andsuch that the annular form flange is in contact with the casting flange,and the apparatus capable of preventing braze alloy contamination of theinterface.

In a further aspect of the present invention, a method of manufacturinga dual alloy turbine wheel comprises the steps of providing a casting, ahub, and a spun metal form, the casting having a casting flange, thespun metal form having a form flange; assembling the casting, the hub,and the spun metal form such that an assembly is produced; applying abraze bead to the assembly such that the braze bead is in contact withthe casting flange and the form flange; vacuum brazing the assembly; andhot isostatic pressing the assembly.

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdrawings, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sectioned dual alloy turbine wheelassembly according to one embodiment of the present invention;

FIG. 2 is a partial cross-section of a dual alloy turbine wheel assemblyaccording to one embodiment of the present invention;

FIG. 3 a is a perspective view of a spun metal form according to anembodiment of the present invention;

FIG. 3 b is a sectional view through B-B in FIG. 3 a;

FIG. 3 c is an inverted perspective view of the spun metal form of FIG.3 a;

FIG. 3 d is a sectional view through D-D in FIG. 3 c;

FIG. 4 is a flow chart depicting the steps of producing a spun metalform according to one embodiment of the present invention;

FIG. 5 is a flow chart depicting the steps of manufacturing a dual alloyturbine wheel according to one embodiment of the present invention;

FIG. 6 is a perspective view of a dual alloy turbine wheel assemblyafter HIP processing according to one embodiment of the presentinvention; and

FIG. 7 is a perspective view of a dual alloy turbine wheel assemblyafter failed HIP processing according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

The present invention generally provides spun metal forms used tomanufacture dual alloy turbine wheels and methods for producing thesame. The spun metal forms produced according to the present inventionmay find beneficial use in many industries including aerospace,automotive, and power plant operations. The present invention may bebeneficial in applications including commercial and military auxiliarypower units (APU), aircraft propulsion, naval propulsion, pumping setsfor gas and oil transmission, and electricity generation. The presentinvention may be useful with any gas turbine engine having a dual alloyturbine wheel.

In one embodiment, the present invention provides a spun metal form 30used to manufacture a dual alloy turbine wheel. Dual alloy turbinewheels may be formed by the diffusion bonding of a casting 31 to a hub32. A HIP process may be utilized to facilitate the diffusion bonding.Prior to HIP processing, the spun metal form 30 of the present inventionmay be assembled together with the casting 31 and the hub 32. The spunmetal form 30 may be brazed to the casting 31 and may be capable ofcreating a vacuum at the future casting/hub interface 36. Unlike theprior art, the present invention may relocate the braze alloy 42 awayfrom the casting/hub interface 36. The spun metal form 30 may preventbraze alloy contamination of the interface between the casting 31 andthe hub 32. Further, unlike the prior art the present invention mayallow for the re-working of defective parts after a braze thermal cycle.

Referring now to FIG. 1, a spun metal form 30 of the present inventionmay be assembled together with a casting 31 and a hub 32. The spun metalform 30 may have a form flange 33 and a form can 39, as better seen inFIGS. 3 a-3 d. The casting 31 may have a casting flange 34. The formflange 33 may be vacuum brazed to the casting flange 34 at a braze joint35. Because the end of form flange 33 that is brazed may be about 0.090inches away from the edge 48 of hub/casting interface 36, braze alloycontamination of hub/casting interface 36 may be prevented.

The braze alloy 42 may be positioned at the flange edge 46, as best seenin FIG. 2. The flange edge 46 may be the outer diameter (rim) of thespun metal form 30. Because spun metal form 30 may conform to the shapeof hub 32 and the portion of the casting 31 that it covers, the brazealloy 42 may wick into the form gap 47 during vacuum brazing. The formgap 47 may be the gap between the spun metal form 30 and the casting 31.The distance between the flange edge 46 and the interface edge 48 may besufficient to prevent the braze alloy 42 from wicking into thehub/casting interface 36. The interface edge 48 may be the outerdiameter (rim) of the hub/casting interface 36. The distance between theflange edge 46 and the interface edge 48 may vary and may depend onfactors including the composition of the braze alloy 42 and thethickness of the form gap 47. The distance between the flange edge 46and the interface edge 48 may be measured through the form gap 47. Thedistance between the flange edge 46 and the interface edge 48 may begreater than the length of a straight line between the flange edge 46and the interface edge 48. In prior art methods, braze alloy 42 wicksinto the hub/casting interface 36 through the interface edge 48. Thecan/flange angle 37 may also contribute to the prevention of braze alloycontamination. The can/flange angle 37, as shown in FIG. 2, may be thearea of the spun metal form 30 where the form flange 33 meets the formcan 39. In prior art methods, the braze joint 35 is located at thehub/casting interface 36 and braze alloy contamination of thehub/casting interface 36 is common. In prior art methods, the brazealloy is wicked into the hub/casting interface during vacuum brazeprocesses.

A spun metal form 30 of the present invention is depicted in FIGS. 3 a-3d. The spun metal form 30 may comprise a form flange 33 and a form can39. The form flange 33 may be integral to the form can 39. The formflange 33 may be annular and may be perpendicular to an axis through thespun metal form 30. The form flange 33 may extend radially out from theform can 39. The form flange 33 and the form can 39 may be manufacturedtogether by known methods. Useful methods for manufacturing a spun metalform 30 may include known spinning methods.

The steps of producing a spun metal form 30 are depicted in FIG. 4. Theprocess may include a step 50 of providing a sheet metal blank, a step51 of spinning the sheet metal blank to shape a spun metal form 30, astep 52 of annealing the spun metal form 30, a step 53 of re-working thespun metal form 30, and a step 54 of passivating the spun metal form 30.

The sheet metal blank of step 50 may comprise a metal alloy sheet.Useful metal alloys may include nickel-based superalloys. Preferredmetal alloys may include INCO 600 series, IN625, and Hast-X. Thedimensions of a useful metal alloy sheet may depend on the desireddimensions of the spun metal form 30. A useful thickness of the metalalloy sheet may vary depending on the composition of the metal alloy andthe desired application. The thickness of useful metal alloy sheets maybe between about 0.032 inches and about 0.100 inches.

The step 51 of spinning the sheet metal blank may utilize known spinningtechniques. Spinning processes are known in the art and have been usedto produce a variety of products possessing rotational symmetry. Knownspinning may comprise clamping a sheet metal blank between a mandrel anda friction block (pad). The sheet metal blank may then be forced overthe mandrel by means of a spinning tool. The sheet metal blank andclamping members may be rotated while the spinning tool is moved on ahorizontal plane on a level with the center of rotation. The forcetransmitted to the sheet metal blank may be partially compressive andpartly flexural in effect. The compressive component may be controlledto avoid thinning the metal locally. Some sheet metal blanks may beprone to work hardening during deformation and may require severalintermediate stages of shaping and annealing, as is known in the art.The sheet metal blank may be spun by hand or by an automatic spinninglathe.

The step 51 may produce a spun metal form 30 that may be near net shape.The geometry of the spun metal form 30 may vary and may depend on thegeometry of the casting 31 and the geometry of the hub 32. Although thedimensions of the spun metal form 30 may vary, a useful spun metal form30 may have dimensions such that the form flange 33 is capable of beingvacuum brazed to the casting flange 34. The form flange 33 may becapable of being brazed to the casting flange 34 at a braze joint 35,such that the braze joint 35 is positioned away from the hub/castinginterface 36. A useful form can 39 may be capable of covering thehub/casting interface 36. A useful spun metal form 30 may be capable ofvacuum sealing the hub/casting interface 36. When the form flange 33 andthe casting flange 34 are vacuum brazed, the hub/casting interface 36may be sealed. The thickness of a useful spun metal form 30 may dependon the composition of the sheet metal blank and the desired application.For example, when the sheet metal blank comprises IN625 and the spunmetal form 30 is used to manufacture a radial dual alloy turbine wheel,a useful thickness of the spun metal form 30 may be between about 0.032inches and about 0.093 inches. The shape of a useful spun metal form 30may vary and may be complimentary to the shape of the casting 31 and hub32. As shown in FIG. 2, the spun metal form 30 may have an inner surface45 that follows the contours of an assembled casting 31 and hub 32.

The step 52 of annealing the spun metal form 30 may comprise knownannealing processes. The step 52 of annealing may comprise solutionannealing. The spun metal form 30 may be annealed by heating in a vacuumfurnace. The temperature and time of heating may vary and may depend onthe composition of the spun metal form 30. For example, when the spunmetal form 30 comprises IN625, the step 52 of annealing may compriseheating the spun metal form 30 to about 2100° F. for about one hour.

After annealing, the spun metal form 30 may be re-worked. The step 53 ofre-working may comprise machining the form flange 33. The form flange 33may be stamped flat by known methods. The form flange 33 may be flat towithin about 0.002 inches as interpreted per ASME Y14.5M. Afterre-working, the form flange 33 may be planar such that the form flange33 may be capable of being positioned flush with the casting flange 34.The form flange 33 may be machined to remove any sharp edges that maycause injury to personnel. Burrs on the form flange 33, which mayinterfere with the vacuum brazing of the form flange 33 to the castingflange 34, may be removed by known machining methods. The form flange 33may be re-worked such that it is capable of being vacuum-brazed to thecasting flange 34.

The steps of producing a spun metal form 30, as depicted in FIG. 4, mayinclude a step 54 of passivating the spun metal form 30 using standardwet chemical techniques. After the step 54 of passivating, the spunmetal form 30 may be used to manufacture a dual alloy object, such as aturbine wheel.

The steps of manufacturing a dual alloy turbine wheel are depicted inFIG. 5. The process may include a step 60 of providing a casting 31; astep 61 of providing a hub 32; a step 62 of cleaning the casting 31 andthe hub 32; a step 63 of assembling a dual alloy turbine wheel assembly38; a step 64 of applying a braze alloy 42; a step 65 of brazing thedual alloy turbine wheel assembly 38; a step 66 of inspecting the dualalloy turbine wheel assembly 38; and a step 67 of hot isostatic pressing(HIP) the dual alloy turbine wheel assembly 38.

The casting 31 of step 60 may comprise any known metal alloy and mayhave a casting chamfer 43 and a casting flange 34. The casting 31 maycomprise an alloy having high creep resistance. Useful metal alloys mayinclude Mar-M-247, INCO 713LC, IN100, IN792, and IN738. The castingchamfer 43, as seen in FIG. 1, may be formed by known machining methods.Machining about 0.125 inches from the casting 31 may form the castingchamfer 43. The casting chamfer 43 may be used to position the spunmetal form 30 during the step 63 of assembling.

The hub 32 of step 61 may comprise any known metal alloy and may have ahub chamfer 44. The hub 32 may comprise an alloy having high tensilestrength. Useful metal alloys may include but are not limited to U720,Astrology PM, or Rene 95. The hub chamfer 44, as seen in FIG. 1, may beformed by known machining methods. Machining about 0.125 inches from thehub 32 may form the hub chamfer 44. The hub chamfer 44 may be used toposition the spun metal form 30 during the step 63 of assembling.

The step 62 of cleaning the casting 31 and the hub 32 may comprise anyknown chemical cleaning methods. After cleaning, the casting 31 and thehub 32 may be assembled together with a spun metal form 30.

The step 63 of assembling a dual alloy turbine wheel assembly 38 maycomprise positioning the casting 31 in contact with the hub 32. A spunmetal form 30 may then be positioned such that the form flange 33 may beflush with the casting flange 34 and such that the spun metal form 30covers the hub/casting interface 36. The casting chamfer 43 and the hubchamfer 44 may be useful for positioning the spun metal form 30. Thestep 63 may occur after the step 44 of passivating the spun metal form30. The step 63 may occur within about eight hours of the step 44 ofpassivating.

The step 64 of applying a braze alloy 42 may comprise applying a bead ofbraze alloy 42 to the form flange 33. The braze alloy 42 may be incontact with the form flange 33 and the casting flange 34. The diameterof a useful bead of braze alloy 42 may be such that the bead is capableof brazing the form flange 33 to the casting flange 34. The diameter ofa useful bead may be such that the braze alloy 42 does not wick into thehub/casting interface 36. The diameter of the bead of braze alloy 42 mayvary and may depend on the application. For example, when manufacturinga radial dual alloy turbine wheel, the diameter of the bead may bebetween about 0.075 inches and about 0.125 inches. Any known brazeapplying techniques and any known braze compositions may be useful withthe present invention.

The step 65 of brazing may comprise vacuum brazing. The step 65 ofbrazing may vacuum seal the hub/casting interface 36. Brazing methodsare known in the art, any of which may be useful with the presentinvention. After brazing, the process may comprise a step 66 ofinspecting the dual alloy turbine wheel assembly 38.

The step 66 of inspecting the assembly 38 may comprise visualinspection. The spun metal form 30 may be deformable and maycompress/crimp during the step 65 of brazing. The spun metal form 30 mayappear concave after the step 65 because the brazing may hold a vacuumseal. A concave appearance of the spun metal form 30 may indicate thatan acceptable vacuum seal has been produced. The concave appearance ofthe spun metal form 30 may be absent from an assembly having a brazeleak. A braze leak may indicate a vacuum seal failure. Unlike prior artmethods, the hub 32 and casting 31 may be re-worked when a braze leak isindicated. This may be because the hub 32 may not be contaminated by thebraze alloy 42.

After the step 66 of inspecting indicates that an acceptable vacuum sealhas been produced, the process may comprise a step 67 of hot isostaticpressing (HIP). Useful HIP methods may include the HIP methods describedin U.S. Pat. No. 4,581,300, which is incorporated herein by reference.Any known HIP methods may be useful with the present invention. The HIPservices of companies, such as Howmet of Whitehall, Mich., may be usefulwith the present invention. Useful HIP methods may comprise pressures ofless than about 25,000 psi at 2,225° F. Strain on the assembly 38 at lowtemperatures may result in damage to the spun metal form 30 anddiffusion bond failure due to vacuum seal leak. At higher HIPtemperatures the spun metal form 30 may be less prone to damage fromcold work. Useful HIP methods may also comprise ceramic HIP supportshaving rounded edges. Supports with rounded edges may prevent the spunmetal forms 30 from being damaged by the supports during HIP.

As shown in FIG. 6, a dual alloy turbine wheel assembly 38 may appearfree of cracks and bulges after HIP processing. This may indicate thatthe vacuum seal was maintained during HIP processing and that theassembly 38 may be acceptable. After HIP processing, a dual alloyturbine wheel assembly 38 may have a bulge 40 and a crack 41, as shownin FIG. 7. This may indicate vacuum seal failure during HIP processingand that the assembly 38 may be unacceptable. The bulge 40 may be due tovacuum loss caused by leakage during HIP. After the step 67 of HIP, thespun metal form 30 and the casting flange 34 may be removed by knownmachining methods.

EXAMPLE 1

Twelve dual alloy turbine wheels were manufactured according to thepresent invention. The spun metal forms 30 comprised IN625. The distancebetween the bead of braze alloy 42 and the interface edge 48 was 0.090inches. The diameter of the bead was 0.075 inches. The castings 31comprised Mar-M-247 and the hubs 32 comprised U720. The HIP processingwas performed by Howmet-Whitehall. The dual alloy turbine wheels werethen inspected for braze alloy contamination of the hub/castinginterface 36. Microprobe analysis was used to examine boron levels atthe hub/casting interface 36. Elevated boron levels were not detected.It was concluded that all twelve dual alloy turbine wheels were free ofbraze alloy contamination of the hub/casting interface.

EXAMPLE 2

Eight specimens from four current production dual alloy turbine wheelsand eight specimens from four dual alloy turbine wheels made using thespun metal form 30 were creep rupture tested. The specimens werecylindrical creep rupture bars machined from the nose of the wheels. Thebond interface was located at the center of the gauge length. Thetesting conditions were 62,000 psi at 1400° F. The mean time of failurefor the current production specimens was 181.8 hours. The mean time offailure for the specimens made using the spun metal form was 218.3hours. The 20% improvement in time to failure may be an additionaladvantage of the present invention. The improvement in time to failuremay be the result of discrete carbide phase along bond interface. Thecurrent production specimens did not have the bond interface carbide.The reason the carbide was not present in the current productionspecimens was not determined.

As can be appreciated by those skilled in the art, the present inventionprovides a spun metal form 30 used to manufacture a dual alloy turbinewheel. Also provided is an expendable metal form that allows forre-working the casting 31 and the hub 32 of an assembly 38 having abraze leak. Moreover, a metal form is provided that is capable of vacuumsealing the hub/casting interface 36 and capable of preventing brazealloy contamination of the hub/casting interface 36. Further, spun metalforms 30 capable of increasing time to failure of dual alloy turbinewheels are provided.

It should be understood, of course, that the foregoing relates topreferred embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

1-33. (Canceled)
 34. A dual alloy assembly manufactured by an apparatus that comprises: a form can including a form flange; said dual alloy object having a hub, a hub/casting interface, a casting, and a casting flange, said form flange vacuum brazed to said casting flange, and said form can preventing braze alloy contamination of said hub/casting interface.
 35. A dual alloy assembly having a bead of braze alloy positioned thereon and manufactured by an apparatus that comprises: a form can including a form flange, a form flange edge, and a form gap; said dual alloy assembly having a hub, a hub/casting interface, an interface edge, a casting, and a casting flange, and said apparatus in contact with said dual alloy assembly such that a distance between said form flange edge and said interface edge, measured through said form gap, is greater than a length of a straight line between said form flange edge and said interface edge.
 36. A dual alloy assembly manufactured by an apparatus that comprises: a form can including a form flange, a form flange edge, and a form gap; said dual alloy assembly having a hub, a casting, and a hub/casting interface, said casting having a casting flange, and said apparatus positioned such that said form flange is vacuum brazed to said casting flange and said form can vacuum seals said hub/casting interface.
 37. A dual alloy assembly manufactured by an apparatus that comprises: a form can; and an annular form flange extending radially out from and integral to said form can, said annular form flange comprising a nickel-based superalloy, said dual alloy turbine wheel having a hub, a hub/casting interface, and a casting flange, said apparatus in contact with said dual alloy turbine wheel such that said form can seals said hub/casting interface and such that said annular form flange is in contact with a portion of said casting flange, and said apparatus prevents braze alloy contamination of said hub/casting interface.
 38. The dual alloy assembly of claim 34, wherein said form can seals said hub/casting interface.
 39. The dual alloy assembly of claim 34, wherein said form flange is planar to within about 0.002 inches (0.005 cm).
 40. The dual alloy assembly of claim 34, wherein said form can comprises a nickel-based superalloy.
 41. The dual alloy assembly of claim 34, wherein said casting has a casting chamfer and said form can is positioned on said casting chamfer.
 42. The dual alloy assembly of claim 34, wherein said hub has a hub chamfer, and said form can is positioned on said hub chamfer.
 43. The dual alloy assembly of claim 34, wherein said form flange is parallel to said casting flange.
 44. The dual alloy assembly of claim 34, wherein said form flange is positioned with respect to said casting flange such that said form flange is flush with said casting flange.
 45. The dual alloy assembly of claim 44, wherein the form can is passivated before being positioned such that the form flange is flush with the casting flange.
 46. The dual alloy assembly of claim 45, wherein the form can is passivated about eight hours before being positioned.
 47. The dual alloy assembly of claim 34, wherein said form flange is annular.
 48. The dual alloy assembly of claim 35, wherein said dual alloy assembly is a dual alloy turbine wheel.
 49. The dual alloy assembly of claim 35, wherein said apparatus comprises a nickel-based superalloy.
 50. The dual alloy assembly of claim 35, wherein said form flange has a thickness between about 0.032 inches (0.08128 cm) and about 0.093 inches (0.23622 cm).
 51. The dual alloy assembly of claim 35, wherein the distance between said form flange edge and said interface edge, measured through said form gap is about 0.090 inches (0.229 cm).
 52. The dual alloy assembly of claim 35, wherein said form flange is annular.
 53. The dual alloy assembly of claim 35, wherein said form flange edge extends about 0.090 inches (0.229 cm) away from said hub/casting interface.
 54. The dual alloy assembly of claim 35, wherein said form can encloses said hub and extends about 0.090 inches (0.229 cm) over said casting, wherein said form can is brazed to said casting.
 55. The dual alloy assembly of claim 35, wherein the bead of braze alloy is applied at about 0.090 inches (0.229 cm) away from said hub/casting interface.
 56. The dual alloy assembly of claim 35, wherein the diameter of the bead of braze alloy is from about 0.075 inches (0.1905 cm) to about 0.125 inches (0.3175 cm).
 57. The dual alloy assembly of claim 35, wherein the bead of braze alloy is in contact with the form flange and the casting flange.
 58. The dual alloy assembly of claim 36, wherein said casting has a casting chamfer.
 59. The dual alloy assembly of claim 36, wherein said hub has a hub chamfer.
 60. The dual alloy assembly of claim 36, wherein said form flange is planar such that said form flange is positioned flush with said casting flange.
 61. The dual alloy assembly of claim 36, wherein said form flange is planar to within about 0.002 inches (0.005 cm).
 62. The dual alloy assembly of claim 36, wherein said form can comprises a nickel-based superalloy.
 63. The dual alloy assembly of claim 36, wherein said casting has a casting chamfer, and said form can is positioned on said casting chamfer.
 64. The dual alloy assembly of claim 36, wherein the hub has a hub chamfer, and the form can is positioned on the hub chamfer.
 65. The dual alloy assembly of claim 36, wherein the form flange is parallel to the casting flange.
 66. The dual alloy assembly of claim 37, wherein the form can conforms to the shape of the hub.
 67. The dual alloy assembly of claim 37, wherein the annular form flange conforms to a shape of the portion of the casting flange.
 68. The dual alloy assembly of claim 37, further comprising a form gap between the form can and the casting.
 69. The dual alloy assembly of claim 37, wherein the dual alloy assembly has an interface edge.
 70. The dual alloy assembly of claim 37, wherein the hub/casting interface has an interface edge, the form flange has a form flange edge, and a distance between the form flange edge and the interface edge is greater than the length of a straight line between the form flange edge and the interface edge.
 71. The dual alloy assembly of claim 37, further comprising a form gap between the form can and the casting.
 72. The dual alloy assembly of claim 70, further comprising a form gap between the form can and the casting, wherein the distance between the form flange edge and the interface edge is measured between the form can and the casting through the form gap.
 73. The dual alloy assembly of claim 37, wherein the hub/casting interface has an interface edge, the form flange has a form flange edge, wherein a distance between the interface edge and the form flange edge, measured through the form gap, is greater than a length of a straight line between the form flange edge and the interface edge.
 74. The dual alloy assembly of claim 37, wherein the form can is integral to the form flange. 